Electric motor control system



y 6, 1950 S. w. HERWALD 2,508,162

ELECTRIC MOTOR CONTROL SYSTEM Filed April 50, 1945 WITNESSES: INVENTOR4;- 4 5c? ymour N H-zrwa/d.

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Patented May 16, 1950 Seymour. Wi. Herwald, Pittsburgh, P'a.,. assignorto Westinghouse Electric Corporation, East Pittsburgh, Pa., acorporation of Pennsylvania Application April-'30; 1945,.Serial No;591,075

(Cl. 3I829') 2. Claims. 1

My invention. relates,. generally, to control systems; and: hasreference inparticular to. remote. controlsystems.

Generally stated,,it isan. object. oi my inventionto v provide a remote.position-controlling system that. is: simple; and-.inexpensiveto.manufacturean'dds easy. to operate.

More. specifically; it is, an. object-of. my invention. to providearremotecontrol systemior positioni-ngv a valve or the like in. any of.a finite. number of..- difierent-positions from aremotev lo.- cation.

It. is; also am important. object of: my invention; to: provide. forselectively determining the. direction. of: operation ofavalve-operating. motor required tomove the valve; to. a desiredposition, and. for maintaining. an operating circuit for the motor.through one; or the other of. alternate circuits. until the valvereaches said. positiom.

Another. object at my invention; is to provide. for separatelydetermining the direction of. operation of a positioning motoroframovableelement and the duration: of. the; operating intervalnecessary' to operateamovable. elementfrom .one positionltoanotherpredetermined position.

Yet-another object. of my invention isto pro.-- v-ide foroperating.avalve orthe like to. any; one of atfinite. number. of different.operating po..- sitions inresponse to definite increments of: volt agein accordance.withithedistance position of the valvevf-rom thedesirediposition.

Still another objector myinvention is to. pro-- vide-ior accuratelypositioning a'movable element from a remote control or operatinglocation in:

response tor-definite: control voltage. increments proportional. to:-the: distance: of. themovable; e1e-- merit-from. a. desired operating;position, by providing. one: operating circuit for. the: positioning,motor hetweenleachloi. a flnitenumber of predeterminedoperatingizpositions.andaanothen'operating. circuit. in; each of said.positions. so=long as the element isremote. from the. desiredposition;

Qther. objects. will,, in. part, be obvious-and will inpart,be-explained hereinafter.

. In-practicing:my inventionin oneform thereof, a directional.- relayis; connectedbetween themovable contact members of a manual position. solecting voltage divider; and" a1 position-indicating: voltage dividerwhichis.- operatively connected: to avalve. that is. to be. remotelyoperatedto. any onezofa finitenumberz of. predeterminedipositions; foroperation. in eachof the positionsinresponseto a difie'rentialvoltagewhich" may exist. between: the moving. contacts at the dividers,dependentv on! the:- valve: being; removed from: the:desired: po.

iii

sition. Each of the voltage dividers has a. finite number of steps ofresistancev corresponding to. the number of. valve positions. Controlrelays operable under the control of the directional re-- lay provide anoperating circuit to'determine the direction of' operation of the valvemotor as it reaches each of. its operating positions. Switch meansinterrupt. the control circuit. each time the valvereachesone of. theoperating positions, thus insuring positive interruption or the control.circuit at the desired operating position For a. morecompleteunderstanding of the natureandscopeof my invention, reference may bemade; to. the. following. detailed description which. may be studied inconnection. with the accompanying. drawing in which the single figureis. a diagrammatic viewv of a remote control system. embodying. theinvention inoneof its forms.

Referring, to the drawing, the reference nu meral I 01' may denote,generally, a remote. control system wherein a. motor H. isutilized tooperate a movable element such as a valve, which may be represented bythe. enclosure I 2, to any onev of. av finite number of. operatingpositions under the control of a remote controltdevice [3.

The. motor H may be ofany suitable type comprising; forexample,.a-direct-current motor having. oppositely related. fieldwindings l4 and I5 for operating. the motor in opposite directions,andanarmature IS. The armature .may be energized from: a suitable sourceof direct current represented-bytheconductors l1 and IS-through acurrent limiting. resistor IS. A switch 20 having operating-windings 2-!and 22 connected. across the fieldwindings l4 and. l5-0f the motor,respectively,v may be: provided. for. shunting. the resistor. iswhenever one of.-. the field. windings is energized.- If desired theresistor 1.9- may be used alone; or the switch 20- may be used withoutvthe resistor for. energizingthe armature IE only whenoneor. the. otherof. the field; windings. l4 and l5 is energized. The motor may beoperatively connected. to the valve I2 in. any suitable manner-,. such.as by. means of. a gear drive designated by the. enclosure 2.4,, and;ashaft. 25.

In order to determine the direction of operationof themotor l-lnecessary to bring the valve l2. to the predetermined position selectedby the controldevice t3; means suchas. the rheostat 28 may lac-provided.forproducing in. conjunctionwith. the; remote control device 13 adifferential voltage dependenton the direction and distance of the valvefrom a desired-position Thor-hem stat 28- may comprise a, movable:contact. army 29 and: a-voltagedividing resistor 30.. The contact armmay be operatively connected to the valve I2 by means of the shaft 25and rotatable to engage any one of a plurality of spaced apartstationary contact members 30a, 3012, etc. These contact members may beconnected at predetermined points to the voltage-dividing resistor 34connected to the direct-current source and may be slightly elongated, soas to provide voltages differing by predetermined increment inaccordance with the actual position of the valve I2, during at leasteach of the operating positions.

The remote control device I3 may likewise comprise a movable contact arm32 and a voltagedividing resistor 34. The arm 32 may be manuallyoperated to a finite number of different operating positionscorresponding to the different operating positions of the valve l2 forengaging a plurality of spaced contact members 34a, 341), etc. Thesecontact members may be connected to the voltage-dividing resistor 34which is connected to the source of direct current, at predeterminedspaced apart points corresponding to those of the stationary contactmembers 30a, 3%, etc.

Operation of the motor Ii may be selectively effected by means ofcontrol relays 3S and which connect the field windings i i and i5,respectively, to the source of direct current. Selective operation ofthe control relays and 38 may be effected by means of a directionalrelay All. The directional relay 40 may be of any suitable type, such asa polarized relay having a mag-- netic core 4! with an operating winding42 connected between the moving contact arms 29 and 32 of the rheostats28 and 13, respectively, The moving armature 43 of the directional relamay comprise a permanent magnet member nor" mally biased to anintermediate position by means such as the springs 34 and disposed to beactuated in one direction or the other to engage stationary contactmembers 45a or 4% depending on the polarity of the differential voltageexisting between the contact arms 32 and 29 each time the valve I2 is inone of the finite number of operating positions.

In order to insure accurate positioning of the valve l2, means such asthe switch device 35 may be provided for interrupting the operatingcircuit of the motor I! each time the valve i2 is in one of the finitenumber of operating positions. This switch device may comprise a movablecontact arm 46 for normally engaging a stationary contact member 45a toprovide an operating circuit for the armature of the valve motor. Meanssuch as the cam 41 may be provided, having a plurality of projections41a, 41b, etc., thereon at spaced intervals corresponding to thedifierent positions of the valve I2. The projections may be arranged toactuate the contact arm 46 to interrupt the operating circuit of themotor II during only a portion of the time that the valve I2 is passingthrough one of the finite number of operating positions and when the arm29 is engaging one or the other of the stationary contact members 30a,301), etc., which have an elongated contact surface.

With the remote control device I3 in the position as shown, no voltagedifferential exists between the contact arms 32 and 29. Accordingly, theoperating winding 42 of the directional relay 40 is deenergized, andneither of the control relays 36 and 38 is energized. The motor II,therefore, remains at rest.

Should it be desired, for example, to move the valve I2 to the thirdoperating position, the movable contact arm 32 of the remote controldevice I3 may be moved to engage its third contact member 340. A voltagedifferential equal to the voltage drop across two of the steps of theresistance 34 will be produced between the contact arms 32 and 29 andthe arm 29 will be at the higher voltage so that a current flows in sucha direction as to energize th operating winding 42 of the directionalrelay 4!] to cause its contact arm 43 to engage the stationary contactmember 40a. An energizing circuit is thereby established for theoperating winding 49 of the control relay 38, extending from conductorI1 through conductor 48, winding 49, normall closed contact members3627, contact member 40a, armature 43 and conductor 5I to conductor I8.At the same time, an energizing circuit is established for the fieldwinding I5 through contact members 36b, contact 40a, arm 4-3 andconductor 5 i. The operating winding 2| of the switch 20 is likewiseenergized and the switch operates to connect the armature IE to theconductors I1 and I8 to start the motor II in a direction to move thecontact arm 29 in a clockwise direction.

As soon as the contact arm 29 leaves stationary contact member 30a, thecircuit hereinbefore described ior the operating winding 42 of thedirection relay is deenergized. However, before this occurs, the cam 41moves from the position shown so that the switch device 45 operates toeffect engagement of its contact members 46 and 45a. A holding circuitis thus provided for the control relay 38 extending from conductor I8,through contact members 45a and 4E, conductor 53, contact member 380;,operating winding 49 and conductor .8 to conductor ll. The field windingit, which is connected in parallel circuit relation with the operatingwinding 49, is likewise maintained energized during the interval betweendisengagement of the moving contact arm 29 with contact member 30a andengagement thereof with contact member 30?).

As soon as the valve I2 reaches the next one of its ope-ratingpositions, the projection 41b on the cam 4'! again operates the switchdevice 45 to interrupt the energizin circuit for the field winding I5 ofthe motor II. However, slightly before this time, the moving contact arm29 of the rheostat 28 engages contact member 3%. Since a difierentialvoltage of the same polarity, equal to the voltage drop across one stepof the resistance 34, still exists between contact arm 32 and contactarm 29, and this increment of voltage is purposely arranged to besufiicient for positive operation of the directional relay 40, theoperating winding 42 of the directional relay 4!] is again energized sothat this relay operates to reenergize the operating winding 49 of thecontrol relay 38. The energizing circuit for the field winding I5 of themotor I I is thereby maintained, despite the fact that the switch device45 opens. As soon as the valve I2 moves from the second of its finitenumber of operating positions, the switch device 45 again closes andprovides a holding circuit for the control relay 38 and an energizingcircuit for the field winding I5 of the valve motor while the contactarm 29 travels between the contacts 392) and 39a.

The motor continues to operate until the valve I2 reaches the next ofits predetermined operating positions. As soon as the valve reaches thisnext operating position, the projection 41c 01 the earn 4'! opens theswitch device 45. Since the contact member 300 is at the same operatingpotential as contact 340 of the remote control device, the operatingwinding 42 of the directional relay 90 remains deenergized. Accordingly,opening of the switch device 45 deenergizes the field winding of thevalve motor as well as operating winding c9 of the control relay 38, andpositively insures stoppage of the motor so that the valve I2 remains inthe operating position corresponding to that selected through operationof the moving contact arm 32 of the remote control device I3. Should thecontact arm 32 be now moved in a counterclockwise direction, thepolarity of the voltage differential between the contact arms 32 and 29would be reversed, so that the directional relay 40 would operate in thereverse direction to close armature 43 and contact 40b and eiiectenergization of the control relay 36 and the field winding M to operatethe motor in the other direction until the valve l2 reaches the positioncorresponding to that of the moving contact arm 32.

From the above-described construction and the accompanying drawing, itwill be apparent that I have provided in a simple and eifective mannerfor positively and definitely controllin the operation of a movableelement, such as a valve or the like, from a remote location. Byperiodically interrupting the operating circuit of the motor driving themovable element in each of the finite number of operating positions andusing a corresponding finite number of distinct increments ofdifferential voltage to control the operation of the motor, positiveoperation thereof to a predetermined position without any overshoot orundershoot may be readily effected. A control system embodying thefeatures of my invention requires a minimum of equipment and is reliablein operation and easy to maintain.

Since certain changes may be made in the above-described constructionand different embodiments of the invention may be made without departingfrom the spirit or scope thereof, it is intended that all of the mattercontained in the above description and shown in the accompanying drawingshall be considered as i1- lustrative and not in a limiting sense.

I claim as my invention:

1. A remote control system for a movin element having a finite number ofdifferent operating positions comprising, means for producing a controlvoltage variable in accordance with the position of the element, meansfor producing an additional control voltage variable in accordance witha desired position of the element, a reversible motor having a pair offield windings and an armature operatively connected to move th element,control means having normally open contact means connected forcontrolling the excitation of the field windings for operating the motorin opposite directions, switch means having contact means operativeintermediate said operating positions of the element connected in seriescircuit relation with the contact means of the control means to providefor excitation of the field windings in conjunction with the controlrelay means, means so connected in a Wheatstone bridge circuit with themeans for producing the control voltage as to be responsive to thepolarity of the differential between the control voltages forcontrolling the control means to selectively provide for excitation ofthe field windings in each of the operating positions remote from thedesired one, and relay means responsive to excitation of the fieldwindings for controlling the energization of the armature.

2. A remote control system for a valve having a finite number ofdistinct operating positions comprising, a reversible direct-currentmotor having an armature mechanically connected to the valve andenergized from a source of direct current and a pair of oppositelyrelated field windings, a rheostat having a moving contact armmechanically operated by the armature for engaging difierent ones of anumber of spaced stationary contact members positioned corresponding tothe operating positions of the valve and connected to spaced points on avoltage divider connected across the source, a remotely located positioncontrol rheostat having a moving contact arm prepositionable to engageany one of a similar number of spaced contact members connected atsimilar intervals to a similar voltage divider connected to the sourcein shunt circuit relation with the aforesaid voltage divider, apolarized relay having an operating winding connected to said voltagedivider through said moving contact arms to provide the balance circuitof a Wheatstone bridge circuit, said polarized relay being selectivelyresponsive to the polarity of a voltage differential between said movingcontacts, switch means having normally closed contact members disposedto be actuated by a cam device operatively connected to the armature ofthe motor and having a plurality of relatively sharply pointed camsurfaces to actuate said contact members to open them each time thevalve reaches one of said operating positions and in substantially thesame position regardless of the direction of movement, a pair of controlrelays having contact means connected in circuit with the switch meansfor selectivel providing an energizing circuit for one or the other ofthe field windings under the control of the polarized relay intermediateeach of the operating positions of the valve, and circuit meansincluding contact members of the polarized relay and the control relaysconnected to selectively provide an energizing circuit for one or theother of the field windings in response to a differential voltagebetween said moving contact arms in an operating position of the valve.

SEYMOUR W. HERWALD.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,669,112 Winter May 8, 19282,177,850 Vogt et al. Oct. 31, 1939 2,295,355 Prescott Sept. 8, 19422,409,895 Phelps Oct. 22, 1946

